Emission of ammonia (NH3) from animal husbandry, and specially from the dairy sector, contributes significantly to acidification and eutrophication, and affects sensitive natural areas. In the nineties Monteny (1998) introduced a mechanistic model to understand and predict the NH3 emissions from cubicle dairy cow houses. Although a limited sensitivity analysis was carried out, we still lack information that essential for further development of the model. Our aim is that the model can predict and assess the NH3 emission from dairy cow houses under practical circumstance. The objective of this research was 1) to determine the relevance and irrelevance of a limited set of input factors, and 2) assess options for further development of the model for use in practice. A full factorial sensitivity analysis was carried out for eight variables related to NH3 emission from a urine puddle on the floor. Relative importance and R2 of the regression model factors were determined. The NH3 emission varied strongly with both high and low emissions. Strongly contributing process variables were puddle pH, initial urea concentration, urination frequency, puddle depth and puddle area. We conclude that deviations in these influencing variables lead to large fluctuations in the NH3 emission, which means that precise quantification of these variables in practice is essential for accurate predictions. Moreover, the results also show that the model may be over-parameterized, having several inputs that seem hardly relevant for the level of NH3 emission.